1. Field of the Invention
The present invention relates to liquid crystal displays and more particularly to the technique of manufacturing a multi-domain liquid crystal display utilizing a photoactivated polymer as an alignment layer for the practice of complimentary domains.
2. Description of the Prior Art
Multi-domain liquid crystal displays are well known in the art. In such displays each pixel or dot (the smallest area which can be independently operated) consists of two halves where one half passes light exactly as if it were 180 degrees rotated with respect to the other. This improves the viewing angle for the dot since the intensity of light passing through a dot is not symmetrical with viewing angle, that is, the peak luminance for various grey scales varies with the viewing angle and this is skewed to one side of the zero angle as the grey scale decreases. It has been found, however, that if a dot is inverted, the opposite change of intensity with viewing angle occurs. That is, intensities that peaked at say a +15 degree viewing angle would now peak at a -15 degree viewing angle. Thus if a dot is divided in half and one half is the inverse of the other, then the two curves which peak at +15 degrees and -15 degrees would merge to produce an average curve which would peak at zero degrees and would be relatively flat on both sides of zero so that the peak intensity would not change much as the eye shifted from -15 degrees to +15 degrees. The same effect is observed at all of the intensities used in creating the grey scale values and a much better display is produced.
All present LCD matrix displays utilize a technique known as "rubbing" on the upper and lower substrate which acts to align the liquid molecules near the surface in a preferred direction. Usually, the upper substrate is "rubbed" in a first direction and the lower substrate is "rubbed" in a direction 90 degrees from the first direction. However, to create two differently directed domains on a single surface, as is required for increasing the viewing angle as above described, the "rubbing" process is difficult to use. While it would be desirable to "rub" each adjacent dot in a different direction, such a procedure is substantially impossible. "Rubbing" has been used to create two domains however by rubbing in one direction over one half of the individual dots in a row and in the other direction over the remaining half. This then produces dots which have two regions which are "rubbed" in opposite directions and this produces the desired effect. This process is described in a paper intitled "Wide-View-Angle Improvements for AMLCDS", published in the Society for Information Display International Symposium Digest of Technical Papers Volume XXIV on pages 266-268.
The two way "rubbing" process is still rather complex and difficult to use because it requires a first "rubbing" in one direction followed by a masking off of half pixels, an etching of the unmasked portions, re-"rubbing" in the other direction over the other half pixels and then removing the masks. Not only is this time consuming and expensive, but a border area between the two "rubbings" results in loss of active area.
In an article entitled "Surface-Induced Parallel Alignment of Liquid Crystals My Linearly Polymerized Photopolymers" printed in the Journal of Applied Physics, Volume 31, (1992) Pages 2155-2164, a technique of photopolymerization of polymer-coated substrate with linearly polarized light is shown to induce an anisotropic, uniaxial orientation of polymer molecules. The resulting anisotropic dispersive surface interaction forces are shown to align adjacent liquid crystals parallel. This produces the same effect as "rubbing" and it is suggested that the technique could be used on the upper and lower substrate of the liquid crystal display or, as the Applied Physics article states " . . . to generate homogeneous LC-director pattern with different azimuthal director angles on the same substrate requiring no mechanical treatment.".